ABA AS A MODULATOR OF THE RESPONSE OF PISUM-SATIVUM TO SALT STRESS

Ten-day-old pea plants (Pisum sativum L., cultivar Ran 1) were treated for 24 h with 10(-5)M or 10(-6)M ABA before a salinity treatment with 50 mM NaCl lasting 48 h. The sodium chloride treatment alone resulted in an increase of endogenous proline content, CO2 compensation point, photorespiration and glycolate oxidase activity. Photosynthesis was s ignificantly inhibited. ABA eliminated the inhibitory effect of NaCl a nd the values of the observed parameters were similar to those of the control. (CO2)-C-14 fixation of protoplasts isolated from salt stresse d plants was inhibited about 60%; (CO2)-C-14 fixation by protoplasts i solated from plants treated with ABA before salinization was almost eq ual to that of the control. 10(-5)M or 10(-6)M ABA added exogenously t o the protoplast reaction medium did not affect (CO2)-C-14 fixation. T he reduced CO2 fixation of protoplasts isolated from NaCl stressed pla nts indicated a direct effect of NaCl on the photosynthetic process, w hich was not dependent upon stomatal closure.